This build is aimed at big heals to let the rest of the group do all the dps it wants and not worry about it's life.
We are running most of the support spells on the resto bar for ease of the rotation when you need to switch to buff your party then switch, dual wield swords will be giving us more spell damage and the spells that you want while all the buffs on the resto bar are ticking away, these are the breath of life and damage/shield abilities which you can throw out

With luminous shards + repentance you will be recovering the stamina for everyone in the group when killing multiple mobs and shards providing a synergy for more resource recovery.

Combat prayer is to give everyone a dmg and resist buff while also being a nice aoe heal.

Channeled focus gives you increased healing from the templar passives as well as giving back mana and increasing your resistances. This is what you want to set up before and during a boss fight to keep sustain of magicka up and keep you safer, you can step out of the aura for a decent amount of time before needing to refresh the effects so you can walk around and recast it if you need to keep mobile.

Purifying ritual, this is a life saver in some circumstances, drop it in a place that everyone in your group will be able to use it if needed, when casting it you drop debuffs so dont be afraid to recast if you need to cleanse too. This as well as Rapid Regeneration will be the main dot heal working during every fight so make sure to keep rapid regen up on all of your group and purifying ritual down.

Breath of life is used as a pocket heal but with 3 or more heal dots and sheilds for troubled members in the form of healing ward you shouldn't have an issue with people dropping unless they are getting caught out.

Healing ward will work in a similar way to breath of life in giving the tank or a dps who is getting caught out more effective health while you heal them underneath the shield.

Purifying Light will do a chunk of damage after the end of its duration and scales with damage done to the target during the duration. With a full gear setup this will be around the 20k damage mark which is nothing to sneeze at.

The entropy ability is to grant yourself major sorcery for spell power increase and bigger heals and dmg.

Either entropy or healing ward can be flexed out for harness magicka if you are having issue with magic dmg in a specific dungeon or another damage ability if you have another healer and can lower the strength of your heals in return with clearing the dungeon faster.
Alternatively to get more damage instead you will want to get radiant oppression to drop the boss once its under the 30% mark, use block to cancel if someone needs healing or your buffs are dropping off (staying alive > killing boss a bit faster).


Item Sets:

1: Straight up big heals

5 Julianos -infused on a couple the rest divines (Max magicka enchant)
3 Willpower jewellery, (Magicka recovery enchant)
2 Engine guardian (Max Magicka enchant) -this gives a nice chance at resource regen, this is nice to spam shields

2 Torugs Pact DW Swords
1 Resto (maelstrom)

Julianos

2: Heal/DPS LORD (dat spell power doe)

5 Spell Power Cure - spell damage increase on anyone you overheal (heal past 100%) very good for a group with mages
3 Willpower
2 Molag Kena OR 1Kena and 1 of another Monster Helm set for the 1k hp
-2 Kena will give you the option to go bursty, this isn't the best to sustain heals but if you want to clear fast you can light attack twice to temporarily crush down the mobs. 1kena and 1 of another set will give you similar spell dmg to 2 set spell dmg buffs but you get the 1k hp which is nice.

2 Torugs DW Swords
Maelstrom Resto

Ultimately getting your hands on that maelstrom staff is going to be really useful it has a unique passive of magicka return when overhealing which is going to be happening pretty often with the amount of spell damage and magicka you will end up with.